Two central aminergic model systems in whcih neurotoxin treatment appears to induce axonal remodelling will be studied in parallel. The bulbospinal monoamine system will be used to study (a) 5-HT and NE terminals in the spinal cord, (b) the question of synaptic connections being formed by new sprouts after neurotoxin treatment, and (c) possible regeneration and collateral sprouting in the transected spinal cord. Hypothesized enhancement substances will be tested for their ability to promote growth of aminergic axons across the transection site. The supraoptic commissure and paraventricular nucleus will be used to (a) test effects of neurotoxin-triggered response in neonatal, young adult, and aged animals and (b) obtain ultrastructural correlates of growth, A combination of biostructure (EM; FM; morphometrics; adenylate cyclase histochemistry; HRP) and biochemiitry (assays for cAMP, NE, 5-HT) will be used, with anticipation of neurophysiological and tissue culture correlations as later experimental stages warrant. This broad interdisciplinary approach is expected to provide related and coverging data to help in understanding the process of central and peripheral adrenergic plasticity. Two hypotheses (that SIF cells, or interneurons, can divide in and that SIF cells can sprout and form new functional connections) will be tested directly to establish the extent and characteristics of this catecholamine-rich component of sympathetic ganglia.